Practice Problems: Limiting Reagents (Answer Key)


  1. Take the reaction: NH3 + O2 NO + H2O. In an experiment, 3.25 g of NH3 are allowed to react with 3.50 g of O2.

    a. Which reactant is the limiting reagent?  O2

    b. How many grams of NO are formed?  2.63 g NO

    c. How much of the excess reactant remains after the reaction?  1.76 g NH3 left


  2. If 4.95 g of ethylene (C2H4) are combusted with 3.25 g of oxygen.

    a. What is the limiting reagent?  O2

    b. How many grams of CO2 are formed?  2.98 g CO2


  3. Consider the reaction of C6H6 + Br2 C6H5Br + HBr

    a. What is the theoretical yield of C6H5Br if 42.1 g of C6H6 react with 73.0 g of Br2?  71.6 g C6H5Br

    b. If the actual yield of C6H5Br is 63.6 g, what is the percent yield?  88.8%



  4. Use the following reaction: C4H9OH + NaBr + H2SO4 C4H9Br + NaHSO4 + H2O If 15.0 g of C4H9OH react with 22.4 g of NaBr and 32.7 g of H2SO4 to yield 17.1 g of C4H9Br, what is the percent yield of this reaction?

    61.6%

  5. Silicon nitride (Si3N4) is made by a combining Si and nitrogen gas (N2) at a high temperature. How much (in g) Si is needed to react with an excess of nitrogen gas to prepare 125 g of silicon nitride if the percent yield of the reaction is 95.0%?

    79.1 g Si

  6. Souring of wine occurs when ethanol is converted to acetic acid by oxygen by the following reaction: C2H5OH + O2 CH3COOH + H2O. A 1.00 L bottle of wine, labeled as 8.5% (by volume) ethanol, is found to have a defective seal. Analysis of 1.00 mL showed that there were 0.0274 grams of acetic acid in that 1.00 mL. The density of ethanol is 0.816 g/mL and the density of water is 1.00 g/mL.

    a. What mass of oxygen must have leaked into the bottle?   14.6 g O2

    b. What is the percent yield for the conversion of ethanol to acetic acid if O2 is in excess?   30.3%


  7. A reaction container holds 5.77 g of P4 and 5.77 g of O2.The following reaction occurs: P4 + O2 P4O6. If enough oxygen is available then the P4O6 reacts further: P4O6 + O2 P4O10.

    a. What is the limiting reagent for the formation of P4O10?  O2

    b. What mass of P4O10 is produced?  5.78 g P4O10

    c. What mass of excess reactant is left in the reaction container?  5.76 g P4O6 remain